As regards the automatic capture of cheque amounts, an essential operation consists in detecting and reading out automatically the amounts in figures and in machine-printed or handwritten letters on the cheques. The major difficulty with this operation stems from the fact that the pre-printed background of the cheques is generally complex and is not restored with the required quality by the image sensors currently in use which provide a binary image of the cheques to be scanned.
The problem consisting of eliminating the cheque background and reading out the amounts in figures and in letters in a binary image cannot therefore be resolved satisfactorily by a straightforward conventional technique of binarisation by thresholding, which would attribute to the "background" part pixels with a greyscale value above a previously selected fixed threshold, and to the "amount" part pixels with a greyscale value below this fixed threshold.
The application of conventional binarisation techniques by thresholding leads in fact to numerous errors of interpretation: figures of letters of amounts to be recognised may be mis-filtered as belonging to the pre-printed background of the cheque, and vice versa. Ambiguity between the background and the machine-printed or handwritten text is all the greater since it may be that, on the greyscale image on certain cheques, background pixels are darker than pixels corresponding to the image of the cheque amount.
The purpose of the present invention is to overcome the aforementioned drawbacks by offering adaptive thresholding, particularly adapted to the elimination of the background in images to be processed, and based on the detection of particular two-diminesional geometric configurations, likely to correspond to the machine-printed or handwritten text sought.
The invention may be used just as well to process an entire image, such as a whole cheque image, as to process a sub-image, a particular image field or, more generally, any image portion.